Conventionally, in the manufacture of an energy storage device, there has been known a technique where a container of the energy storage device is formed by applying laser beam welding to the container. In such laser welding where welding is performed by using a laser beam, to suppress oxidation of metal of a part to be welded (welded part) caused by the exposure of the metal with outside air, an inert gas referred to as a shield gas is supplied to the part to be welded thus isolating the part to be welded from air. There has been disclosed a laser welding apparatus where a shield gas is supplied toward the part to be welded from two directions on both sides which sandwich the part to be welded so as to bring the whole part to be welded which is an object to be welded into a shield gas atmosphere (see patent literature 1, for example).